U.S. Pat. No. 5,587,079, incorporated herein by reference, discloses processes for treating solutions containing sulfate and metal ions, including processes in which bacteria are used to provide hydrogen sulphide for treating solutions containing metal ions. It has been suggested that to efficiently precipitate nickel sulphides from aqueous solutions, it is necessary to use low pH and elevated temperatures and pressures, as is disclosed in Canadian Patent No. 540,517 and U.S. Pat. Nos. 4,110,400 and 4,547,347.
There remains a need for alternative processes for treating aqueous solutions containing dissolved metals.